Recently, in association with developments of Internet related techniques and/or mobile communication techniques, electrical commerce making use of cell phones, PDA (Personal Digital Assistance), and the like have been widespread.
For example, a system allowing a user to download application programs for a PDA through a computer network and to use the programs or the like, for free of charge or for value, within a predetermined period have been considered.
There has been suggested a method for restricting the usage period of the downloaded contents. An example of such a means is disclosed in Japanese Patent Provisional Publication No. HEI 10-222579. According to the publication, a restrict means known as “time bomb” is incorporated in the application, which restricts the usage of the application when the allowed time period has expired. The usage period is typically determined by counting the period since the date and time, which are obtained from the clock of the PDA, when the application is installed in the PDA.
Another method is suggested, in which a counter is incremented upon every start-up of the application, and the usage of the application is prohibited when the counter exceeds a predetermined count value.
In the above method of managing the expiration of usage of the application, there exist problems as indicated below.
Firstly, the means of restricting the usage of the application should be incorporated in the individual application by the vender thereof, which increases burden of the vender.
Further, the initial date of reckoning is determined by a user (client) and cannot be determined by the vender. Therefore, the vender is unable to obtain the expiration information correctly, and is unable to inspect whether the expiration date is held correctly by each client.
When the usage is restricted based on the number of start-ups, it is only managed at the client side (i.e., by the PDA) since the vender of a server cannot obtain the number of start-ups of the application from each client. Thus, according to this method, the server or the vender cannot manage the expiration of the application. Further, if the application is configured to update data related to the expiration period in the PDA, it can easily be recognized by the client. If an ill-willed user rewrites the data related to the expiration, the application may be used even if the number of start-ups exceeds the upper limit.
Furthermore, in a conventional system in which a program is sold by user's downloading (i.e., when the application is downloaded, billing is executed), the following problem may occur. That is, when the user is downloading the application, the downloading process may be aborted due to some reason such as a communication error. Therefore, for the server, it is necessary to confirm that the download is successfully completed, which requires a troublesome procedure for the server. There is a system which allows re-downloading of the application for a certain period in case the previous downloading was unsuccessful. In such a case, however, if the specified period is expired, the user cannot download the application again. In such a case, even if the user has paid for the application, he/she cannot download the application for free.